This study will assess the hemodynamic consequences (aortic pressures, right atrial pressure, cardiac output, left ventricular stroke work index stroke volume, mixed venous oxygen saturation, pulmonary and systemic vascular resistance and urinary output) of two methods of weaning counterpulsation (assist rate reduction - Pattern A and balloon volume reduction - Pattern B) in heart failure. Currently, nurses weaning intraaortic balloon counterpulsation rely on clinical experience and or a "preferred method" without the benefit of empirically based data. The specific aims of this study include: 1. determine the effect of balloon assist rate reduction (Weaning Pattern A) on hemodynamics; 2. determine the effect of balloon volume reduction (Weaning Pattern B) on hemodynamics; and 3. Determine the interaction effect of balloon assist rate reduction and balloon volume reduction in counterpulsation on hemodynamics. Using 24 dogs, a REPEATED MEASURES CROSSOVER DESIGN will be used for the conduct of the study.